The present invention relates to a so-called exhaust gas recycling apparatus of vehicles, which is referred to as EGR apparatus for short. More particularly it relates to a system wherein the EGR apparatus is made of an aluminum alloy which system is successful in against resisting against corrosion.
In an EGR system in accordance with this invention, a recycling method of the exhaust gas of an internal combustion engine into the gas in-take or suction side is adopted; the recycling system is so constructed that the degree of opening of an exhaust gas recycling valve (hereinafter simply referred to as an EGR valve) can be regulated depending on the intensity of the negative pressure producted in the carburetor.
Exhaust gas from the internal combustion engine generally contains, to say nothing of HC (hydro-carbon), CO, and/or NO.sub.x which are designated as sources of public nuisance or air pollution to be controlled, traces of other chemically active components. In the EGR system, through which extremely high temperature (normally 200.degree. - 300.degree. C) exhaust gases from the engine pass immediately after exit from the engine, the active components may cause acute chemical actions. Heat-resistance as well as corrosion-resistance are therefore required as essential features for the EGR system which is subjected to the abovementioned conditions. In the past when such EGR systems were made of ferrous materials, few problems occurred, since countermeasures therefor have been relatively easy to find. The recently prevailing requirements in the design of vehicles for lightening their weight has brought about a tendency of using light metals in the EGR system, at least in the EGR valve or exhaust gas cooler, which is comparatively great in weight. At first, various kinds of aluminum alloys were tried one after another, but all of them turned out after all to be susceptible to rapid corrosion. Effective measures for enhancing both heat-resistance and corrosion-resistance have been, although very hard, imminent requirements.